Giardia lamblia is a human pathogen afflicting impoverished nations, and the most common cause of outbreaks of diarrhea in the United States. Giardia has been classified by the CDC as a category B bioterrorism organism. The favored anti giardiasis drugs in the US are metronidazole or tinidazole, compounds that have undesirable side effects. Moreover, increasing resistance to drug regimes and recurrence are a concern. It is thus clear that alternative drug treatments are needed. We have developed a bioluminescence Giarida viability assay based on the trophozoites ATP content that is suitable for high throughput screening and miniaturized the assay for compound screening in 1536-well plates. We propose to screen the NIH compound library and investigate the selectivity of hit compounds using initially CHO cells and later CACO-2 cells. The minimum lethal concentration of selective compounds exhibiting low IC50 will be determined by re- growth experiments. For a few top hits, identification of the Giardia target will be undertaken and if successful, advanced to structure-based compound optimization. PUBLIC HEALTH RELEVANCE: Giardia lamblia is a human pathogen afflicting billions of people annually and a category B bioterrorism organism. Giardiasis treatments have undesirable side effects, recurrence, and increasing drug resistance. To facilitate discovery of better drugs, we have developed a Giardia viability assay and miniaturized it for high throughput compound screening. This assay will be used to screen the NIH compound library and identify compounds that kill Giardia trophozoites.